Such a lithotriptor is disclosed for example in the brochure "MFL 5000" by Messrs. C. H. F. Moller (Phillips). In that lithotriptor, an X-ray system locates a concretion as is required before it can be destroyed by ultrasonic shock waves. After the concretion has been successfully located, its three dimensional coordinates are electronically determined. A complicated electronic and mechanical system is then used to guide the transducer until its focus lies in the region defined by the three-dimensional coordinates that have been determined. The ultrasonic shock waves can only then be applied to the concretion to medical advantage.